This invention relates to the art of post-mix beverage dispensers and, more particularly, to improved solenoid actuated valves for controlling the flow of a diluent and a syrup which are mixed to produce the beverage to be dispensed.
Post-mix beverage dispensers are well known and, for example, are basically of the structure and operation shown in U.S. Pat. No. 4,266,626 to Brown et al, the disclosure of which is incorporated herein by reference for background purposes. In a post-mix dispenser of the foregoing character, a diluent such as soda water and a syrup flow into the body of the dispenser through separate inlet passageways and across corresponding flow rate control valves toward a mixing area which is generally associated with the nozzle of the dispenser. Flow from the inlets to the nozzle is controlled by a pair of solenoid valves, one for each of the liquids, and a drink is dispensed by pressing a receptacle such as a cup against a control lever which actuates a microswitch by which the solenoid coils are simultaneously energized. Such energization of the solenoid coils opens the vales, whereupon the diluent and syrup flow across the corresponding valve seat and into the nozzle wherein they mix and flow into the receptacle.
Each of the solenoid valves, typically, includes a coil and armature coaxial with the valve seat, and the end of the armature facing the valve seat is provided with a valve element which engages and disengages the valve seat to respectively close and open the valve to the flow of liquid therethrough. The valves are normally closed and are biased to the closed position by a corresponding coil spring and the pressure of the diluent or syrup acting against the valve element and/or armature in a corresponding chamber on the upstream side of the valve seat. The chamber is in constant flow communication with the corresponding source which is under pressure, whereby the liquid in the chamber is under constant pressure.
The power of the solenoid required to open the valve is dependent, in part, on the closing force of the biasing spring and the closing force against the valve element and/or armature by the pressure of the liquid in the chamber on the upstream side of the valve seat. Especially in connection with the diluent, which may be under a pressure from 60 to 125 psi, the closing forces are considerable. Moreover, upon opening of the valve, the sudden flow of the liquid across the valve seat is turbulent and can result in the loss of carbonation which is undesirable in that it is an objective of such post-mix dispensers to dispense the drink with the highest amount of carbonation possible. It will be appreciated that the required power for opening the solenoid valve increases with higher liquid pressures, as does the turbulence of flow when the valve is opened, whereby the potential for loss of carbonation in connection with the soda water also increases with increasing pressure. In connection with both syrup and diluent flow, turbulence of flow across the valve seat restricts the flow and thus can reduce the quantity of flow of either or both during the period that the valves are open. This makes it difficult to consistently obtain the desired mix of syrup and diluent for the beverage being dispensed.